This work assessed the state of our knowledge on marine biodiversity globally based on the world's largest biogeographic database, the Ocean Biogeographic Information System (OBIS). OBIS contains 112,514 distinct marine species mainly originating from three major taxonomic groups: Crustacea, Mollusca, and Pisces. These three groups represent more than half of all data in OBIS, resulting in a high incompleteness of other taxonomic groups. Different oceanic regions show the same pattern: the same three groups were highly represented. Taxonomic gaps remain for other groups. Also in terms of depth, and geographical coverage gaps were found. Large parts of the open ocean are under sampled and do not represent a similar apparent species richness as other open ocean regions with higher sampling effort and completeness. The Chao2 species richness allowed the assessment of the completeness of OBIS data. Coastal areas mostly deliver reliable estimators, but the completeness stays low. These results can provide baselines for future assessments such as the World Ocean Assessment of the United Nations and can guide policy makers in setting priorities towards enhancing our knowledgebase by targeting gaps in taxonomy, ocean depth, and geographical coverage.The OBIS database also provided insights in species distribution changes. A poleward shift was detected with a narrowing range for tropical and temperate species. However, first results showed that polar shifted on average a movement towards the equator and an expanding range. Still, only the range for tropical species differed greatly, where a clear shift away from the equator was seen.

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